Coordinated control of renewable electric generation resource and charge storage device

ABSTRACT

A method includes obtaining a state of charge (SOC) schedule for an energy storage device and a time-dependent forecast of electrical energy production by a renewable electrical energy generation resource; generating a time-varying charge/discharge control signal for the electrical energy storage device based on the time-dependent forecast of electrical energy production, wherein the time-varying charge/discharge control signal is configured to maintain an average SOC of the energy storage device as low as possible while satisfying the SOC schedule; and controlling charging and discharging of the energy storage device with the time-varying charge/discharge control signal.

CROSS-REFERENCE TO RELATED APPLICATION(S)

This application claims the benefit of priority as a continuation toU.S. patent application Ser. No. 16/579,282, filed Sep. 23, 2019, whichclaims the benefit of priority to U.S. Provisional Patent ApplicationNo. 62/802,928 filed on Feb. 8, 2019, each of which is incorporated byreference herein.

TECHNICAL FIELD

Subject matter herein relates to methods for controlling renewableelectrical energy generation resources and associated electrical energycharge storage devices in a coordinated fashion, such as for supplyingan aggregated power output to an electrical grid.

BACKGROUND

A substantial increase of renewable electric generation resources, suchas solar photovoltaic (PV) and wind power generators, has taken place inrecent years. The unsteady nature of solar and wind generation due tonatural and meteorological conditions can result in network frequencyand voltage deviations. As renewable electric generation resources startto provide a greater percentage of electrical supply and displacetraditional base-load electrical generation units such as coal-fired andnuclear-powered units, technical challenges are introduced, such as gridinterconnection, power quality, reliability, stability, protection, andgeneration dispatch and control. The intermittent nature of solar andwind generation and rapid fluctuation in their output make energystorage devices (such as a battery energy storage system or BESS)attractive to enhance compatibility with electrical grids.

Co-locating renewable electric generation and electrical energy storagedevices may provide cost savings by reducing costs related to sitepreparation, land acquisition, permitting, interconnection, installationlabor, hardware, and overhead. Additionally, tax savings may result,typically if the electrical energy storage devices are subject to beingcharged exclusively from on-site renewable electric generationresources.

Various considerations may affect utilization of a BESS. Lithium-basedbatteries can degrade at an accelerated rate when at or near a fullcharge capacity. Grid operators seeking to dispatch an integratedrenewable electric generation and charge storage facility may requireattainment of specific battery state of charge (SOC) conditions atparticular times in a given day (with SOC being generally defined as thepercentage of the full capacity of a battery that is still available forfurther discharge). Once a battery is at 100% SOC, it is also unable toabsorb rapid increases in electric power output of an associatedrenewable electric generation resource, such that any excess powergeneration not able to be accepted by an electrical grid may undesirablyneed to be dissipated as heat by clipping in a power inverter.

In view of the foregoing, need exists for improved methods forcontrolling renewable electrical energy generation resources andassociated electrical energy charge storage devices.

SUMMARY

The present disclosure relates in various aspects to a method forcoordinated control of a renewable electrical energy generation resourceand an electrical energy storage device, with the method utilizing atime-dependent forecast of electrical energy production by the renewableelectrical energy generation resource and state of charge (SOC) schedulefor the electrical energy storage, wherein both of the electrical energyproduction forecast and the SOC schedule may be subject to change.

In one aspect, the disclosure relates to a method for controlling (i) arenewable electrical energy generation resource and (ii) an electricalenergy storage device chargeable with electric power produced by therenewable electrical energy generation resource. The method comprisesutilizing (A) a time-dependent forecast of electrical energy productionby the renewable electrical energy generation resource and (B) a stateof charge (SOC) schedule for the electrical energy storage deviceincluding at least one SOC target value, to generate a time-varyingcharge/discharge control signal for the electrical energy storagedevice, wherein the time-varying charge/discharge control signal isconfigured to ensure that the SOC schedule is satisfied by charging atthe average rate necessary to meet the SOC target value, whileperiodically updating the generation of the time-varyingcharge/discharge control signal based upon at least one of an updatedtime-dependent forecast of electrical energy production or an updatedSOC schedule.

In certain embodiments, the electrical energy storage device is chargedexclusively from the renewable electrical energy generation resource.

In certain embodiments, the method further comprises altering thetime-varying charge/discharge control signal responsive to a differencebetween forecasted production and the actual production of at least oneelectric generation facility to ensure that the SOC schedule issatisfied.

In certain embodiments, the time-varying charge/discharge control signalis permitted to change only once within a configurable refresh period,to keep aggregated power output of a RES-ESS facility during the refreshperiod, thereby enabling participation in energy markets and/or energybalance markets.

In certain embodiments, the method further comprises periodicallyupdating the generation of the time-varying control signal uponexpiration of a refresh period, wherein the periodic updating comprisescomputing and using a new basepoint value for aggregated energy suppliedfrom the renewable electrical energy generation resource and theelectrical energy storage device to an electrical grid upon expirationof the refresh period. In certain embodiments, the refresh period isconfigurable, and the time-varying charge/discharge control signal ispermitted to change no more than once per refresh period.

In certain embodiments, the time-varying charge/discharge control signalis further configured to increase the value of the time-varyingcharge/discharge control signal during periods of increased relativeproduction of the renewable electrical energy generation resource tosmooth an aggregated power output supplied to the electrical grid by therenewable electrical energy generation resource and the electricalenergy storage device, while ensuring that the SOC schedule issatisfied.

In certain embodiments, the time-varying charge/discharge control signalis susceptible to being varied by adoption of one or more control modesof a plurality of control modes, and wherein the method furthercomprises: for each control mode of the plurality of control modes,generating a plurality of control signal candidate values including anupper bound value, a lower bound value, and an ideal value; andidentifying an intersection of control signal candidate values amongmultiple control modes, or selecting an ideal value for a control modeof highest priority, to generate the time-varying charge/dischargecontrol signal.

In certain embodiments, the plurality of control modes comprises two ormore of the following modes: Charge-Discharge mode, Coordinate ChargeDischarge mode, Active Power Limit mode, Active Power Response mode,Active Power Smoothing mode, and Pricing Signal mode.

In certain embodiments, the plurality of control modes further comprisesat least one of the following modes: Volt-Watt mode, Frequency-WattCurve mode, and Automatic Generation Control mode.

In certain embodiments, the renewable electrical energy generationresource comprises a photovoltaic array, the electrical energy storagedevice comprises a battery array, and the time-dependent forecast ofelectrical energy production comprises a solar production forecast.

In certain embodiments, the renewable electrical energy generationresource comprises at least one wind turbine, the electrical energystorage device comprises a battery array, and the time-dependentforecast of electrical energy production comprises a wind productionforecast.

In certain embodiments, the time-dependent forecast of electrical energyproduction comprises an ensemble based on of two or more of thefollowing: on-site sky imaging, satellite imaging, and meteorologicalmodeling.

In certain embodiments, wherein the time-dependent forecast ofelectrical energy production comprises a refresh rate that determineshow often a new basepoint value for aggregated photovoltaic plus storageenergy supplied to an electric grid (PV+S output basepoint value) iscomputed. In certain embodiments, a pre-existing PV+S Output value isused until a new PV+S output basepoint value is computed.

In another aspects, the disclosure relates to a non-transitory computerreadable medium containing program instructions for controlling, by atleast one processor, (i) a renewable electrical energy generationresource and (ii) an electrical energy storage device chargeable withelectric power produced by the renewable electrical energy generationresource, the method comprising utilizing, by the at least oneprocessor, (A) a time-dependent forecast of electrical energy productionby the renewable electrical energy generation resource and (B) a stateof charge (SOC) schedule for the electrical energy storage deviceincluding at least one SOC target value, to generate a time-varyingcharge/discharge control signal for the electrical energy storagedevice, wherein the time-varying charge/discharge control signal isconfigured to ensure that the SOC schedule is satisfied by charging atthe average rate necessary to meet the SOC target schedule, whileperiodically updating the generation of the time-varyingcharge/discharge control signal based upon at least one of an updatedtime-dependent forecast of electrical energy production or an updatedSOC schedule. In certain embodiments, the program instructions containedin the computer readable medium may be configured to perform additionalmethod steps as disclosed herein.

In another aspect, any of the foregoing aspects, and/or various separateaspects and features as described herein, may be combined for additionaladvantage. Any of the various features and elements as disclosed hereinmay be combined with one or more other disclosed features and elementsunless indicated to the contrary herein.

Other aspects, features and embodiments of the present disclosure willbe more fully apparent from the ensuing disclosure and appended claims.

BRIEF DESCRIPTION OF DRAWINGS

The accompanying drawings incorporated in and forming a part of thisspecification illustrate several aspects of the disclosure, and togetherwith the description serve to explain the principles of the disclosure.

FIG. 1A is a schematic diagram showing interconnections between variouscomponents of an AC coupled metering and control system for controllinga renewable energy source and energy storage system (e.g., aphotovoltaic (PV) array and a battery array chargeable with electricpower produced by the PV array) according to one embodiment.

FIG. 1B is a schematic diagram showing certain components of the ACcoupled metering and control system of FIG. 1A.

FIG. 2 is a block diagram for a processor-based energy dispatch controlsystem for dispatching a renewable electrical energy generation resourceand an electrical energy storage device chargeable with electric powerproduced by the renewable electrical energy generation resourceaccording to one embodiment.

FIG. 3 is a logic diagram for charging an electrical energy storagedevice to reach a state of charge (SOC) target value using a system thatincludes a PV array and a battery array chargeable with electric powerproduced by the PV array according to one embodiment.

FIG. 4 is a logic diagram for discharging an electrical energy storagedevice using a system that includes a PV array and a battery arraychargeable with electric power produced by the PV array according to oneembodiment.

FIG. 5 is a modeled output plot for a system including a renewableelectrical energy generation resource (RES) and an electrical energystorage device (ESS) chargeable with electric power produced by therenewable electrical energy generation resource, when controlled by amethod as disclosed herein, for a period between 06:00 and 21:00 of asingle day.

FIG. 6 is a first diagram illustrating a serial (or stacking)arrangement of different control modes, with each control mode includingmultiple control signal candidate values, and with the seriallyconnected control modes configured to produce a basepoint signal usableas a single active power command.

FIGS. 7A-7E embody tables identifying control signal candidate valuesfor multiple serially connected control modes and a net output valueaccording to different examples.

FIG. 8 is an exemplary output plot for system including a renewableelectrical energy generation resource (RES) and an electrical energystorage device (ESS) chargeable with electric power produced by therenewable electrical energy generation resource, when controlled by amethod utilizing different combinations of connected control modes atdifferent times according to one embodiment.

FIG. 9 is a second diagram illustrating a serial (or stacking)arrangement of different control modes including multiple control signalcandidate values, including serially connected basepoint andnon-basepoint control modes configured to produce a single active powercommand.

FIG. 10 is schematic diagram of a generalized representation of acomputer system that can be included as one or more components of asystem for controlling a renewable electrical energy generation resourceand an electrical energy storage device chargeable with electric powerproduced by the renewable electrical energy generation resource,according to one embodiment.

FIG. 11A is a modeled output plot for a system including a renewableelectrical energy generation resource (RES) and an electrical energystorage device (ESS) chargeable with electric power produced by the RES,when controlled by a method as disclosed herein but without aconfigurable refresh period, for a period including 06:00 to 21:00 of asingle day.

FIG. 11B is a modeled output plot for the same RES-ESS system and perioddepicted in FIG. 11A, when controlled by a method disclosed herein withutilization of a 30 minute refresh period, in which basepoint value isrecalculated once every 30 minutes.

FIGS. 12A and 12B provided modeled output plots for a system including arenewable electrical energy generation resource (RES) and an electricalenergy storage device (ESS) chargeable with electric power produced bythe RES, each utilizing a refresh period, but with FIG. 12B using astatic window that takes into account the solar production forecast fromthe beginning of the control period until the end in order to meet a SOCtarget schedule.

DETAILED DESCRIPTION

The embodiments set forth below represent the necessary information toenable those skilled in the art to practice the embodiments andillustrate the best mode of practicing the embodiments. Upon reading thefollowing description in light of the accompanying drawing figures,those skilled in the art will understand the concepts of the disclosureand will recognize applications of these concepts not particularlyaddressed herein, but it should be understood that such concepts andapplications are intended to fall within the scope of the disclosure andthe accompanying claims.

It will be understood that, although the terms “first,” “second,” etc.may be used herein to describe various elements, these elements shouldnot be limited by these terms. These terms are only used to distinguishone element from another. For example, a first element could be termed asecond element, and, similarly, a second element could be termed a firstelement, without departing from the scope of the present disclosure. Asused herein, the term “and/or” includes any and all combinations of oneor more of the associated listed items.

The terminology used herein is for the purpose of describing particularembodiments only and is not intended to be limiting of the disclosure.As used herein, the singular forms “a,” “an,” and “the” are intended toinclude the plural forms as well, unless the context clearly indicatesotherwise. It will be further understood that the terms “comprises,”“comprising,” “includes,” and/or “including” when used herein specifythe presence of stated features, integers, steps, operations, elements,and/or components, but do not preclude the presence or addition of oneor more other features, integers, steps, operations, elements,components, and/or groups thereof.

Unless otherwise defined, all terms (including technical and scientificterms) used herein have the same meaning as commonly understood by oneof ordinary skill in the art to which this disclosure belongs. It willbe further understood that terms used herein should be interpreted ashaving a meaning that is consistent with their meaning in the context ofthis specification and the relevant art and will not be interpreted inan idealized or overly formal sense unless expressly so defined herein.

The Modular Energy Storage Association (MESA) recently released aspecification titled “DNP3 Application Note AN2018-001—DNP3 Profile forCommunications with Distributed Energy Resources,” wherein “DNP” refersto Distributed Network Protocol. This MESA specification defines controlmodes for standalone energy storage systems. One of these control modesis called “Coordinated Charge/Discharge (CCD).” In CCD mode, an EnergyStorage System (ESS) is given a schedule by which to reach a certainstate of charge (SOC) by charging or discharging. For example, an ESSmay be instructed to reach 100% SOC by 5 PM, and then reach 10% SOC by10 PM. This schedule may be repeated every day. An ESS may be co-locatedand controlled in tandem with a photovoltaic (PV) electricity generatoror any other renewable energy source.

Embodiments described in the present application document provide ahighly desirable implementation of CCD mode for an integrated renewableenergy source (“RES”) (e.g., PV, wind, etc.) and energy storage system(“ESS”) facility or plant, wherein the combination may be referred tohere as RES-ESS or a RES-ESS facility (of which a photovoltaic plusstorage or “PV+S” facility is a subset). A RES-ESS facility will reachthe desired SOC when charging. In certain embodiments, a RES-ESSfacility will reach the desired SOC by prioritizing charging at timeswhen RES generation is high. For example, an ESS may be charged morewhen more RES generation is available, and an ESS may be charged less(or not at all) when RES generation is limited. In certain embodiments,a RES-ESS facility will charge the ESS only from the RES, so that amaximum investment tax credit (ITC) can be utilized to reduce theeffective cost of the facility. In certain embodiments, the ESS mayadditionally be charged from an electric grid connected to the RES-ESSfacility.

Methods disclosed herein may be enabled by integrating accuraterenewable energy production forecasts (e.g., for PV or wind production)into the implementation of CCD mode. In certain embodiments, a periodicmaximum SOC value specified in a SOC schedule (e.g., the maximum SOC fora particular day, wherein such value may be less than 100%) is attainedas late as possible to enable maximal recovery of excess energy thatwould otherwise be clipped by a DC/AC inverter. In certain embodiments,a periodic maximum SOC value specified in a SOC schedule may be attainedas late as possible by charging the ESS at the lowest average chargingrate that will satisfy the SOC schedule; in certain embodiments, thismay involve maintaining the minimum possible average SOC that stillenables satisfaction of the SOC schedule. By charging an ESS as late aspossible, headroom remains in the ESS to implement ancillary servicesthat further increase the revenue generated by the RES-ESS plant.

One benefit of maintaining average SOC of an ESS as low as possible isthat it may prolong the life of batteries associated with the ESS, sinceit is widely recognized that various types of lithium polymer batteriesexhibit increased degradation with maintenance of a high average SOC.

Utilization of methods disclosed herein may also beneficially smooth theoutput of a RES-ESS plant, thereby providing a very desirable attributefor utilities and grid operators. A naïve implementation of CCD mode(i.e., without benefit of reading the present disclosure) would involvegreedy charging, to charge as soon as possible to reach the SOC target,but such a strategy may increase the likelihood of potentially wastingclipped energy for a DC coupled storage system (thereby increasing theeffective cost of operating the plant), or result in a non-smooth plantoutput for an AC coupled RES-ESS. Moreover, as mentioned previously,maintaining a high SOC for a long period of time would be expected toincrease degradation of an ESS over its lifetime. A slightly moreefficient implementation of CCD mode may interpolate the charging suchthat the RES-ESS facility charges the ESS linearly between the currenttime and the SOC target time. This proposed strategy suffers from thedrawback that a desired SOC may be not satisfied if the RES-ESS facilityis unable to produce energy according to the day's renewable energyproduction forecast.

In certain embodiments, a time-dependent forecast of electrical energyproduction may be based on on-site sky imaging (e.g., using a camera),satellite imaging, or meteorological modeling. In certain embodiments, atime-dependent forecast of electrical energy production may be based onan ensemble of two or more (or all three) of on-site sky imaging (e.g.,using a camera), satellite imaging, and meteorological modeling.

FIG. 1A is a schematic diagram showing interconnections between variouscomponents of an AC coupled metering and control system 10 forcontrolling a renewable electrical energy generation device 14 includingmultiple generation units 14A-14N (such as a photovoltaic (PV) arrayincluding photovoltaic units) and an energy storage device 24 includingmultiple energy storage units 24A-24N (such as a battery array includingbattery units) chargeable with electric power produced by the renewableelectrical energy generation device 14 in a RES-ESS facility 11according to one embodiment. The RES-ESS facility 11 may combine arenewable electrical energy generation device 14 (e.g., such as an arrayof PV panels, wind turbines, or the like), and an energy storage device24 (e.g., an array of lithium-based batteries) that may be coupled to asingle substation 30 and/or located in a single property, area, orstructure.

FIG. 1A illustrates an AC-coupled RES-ESS facility 11 that usesinverters 16, 26 to convert DC power produced by a renewable electricalenergy generation device 14 (e.g., a PV array in certain embodiments) orpower released by the energy storage device 24 to AC power for couplingto an AC electrical grid 34), but in certain embodiments, the RES-ESSfacility 11 may embody a DC coupled RES-ESS facility. In certainembodiments, an energy storage device 24 may include at least one of (ora combination of) batteries 24A, 24B using various constructions andchemistries, capacitors, or mechanical energy storage devices such asflywheels or pumped-hydro installations. In certain embodiments, anenergy storage device 24 may include at least one hydrolysis unit (e.g.,configured to electrolyze water to release hydrogen) and a hydrogenstorage unit (e.g., adsorbent media for releasably binding hydrogen,storage vessels, and/or reversible chemical reactant vessels or beds).In certain embodiments, an energy storage device 24 may consist ofelectrical charge storage devices such as batteries, optionallyaugmented with capacitors.

In certain embodiments, a RES-ESS dispatcher unit 36 has the ability tocontrol the charge or discharge of the energy storage device 24 (e.g.,batteries) by communicating with an ESS controller 22, which may belocated in the RES-ESS facility 11. A RES SCADA (supervisory control anddata acquisition) controller 12 is operatively coupled with RESinverters 16 associated with the renewable electrical energy generationdevice 14 (optionally embodied in a PV array), and the ESS controller 22is operatively coupled with ESS inverters 26 associated with the energystorage device 24, with both the RES SCADA controller 12 and the ESScontroller 22 being in communication with the RES-ESS dispatcher unit36. In certain embodiments, a utility control center 38 (e.g., of anelectric power utility or grid operator) may communicate with theRES-ESS dispatcher unit 36 using DNP3 and set different configurationoptions. Additionally, the RES-ESS dispatcher unit 36 receives (orgenerates) an accurate renewable generation forecast (e.g., solargeneration forecast) that it uses to implement the CCD and other controlmodes. As shown in FIG. 1A, certain embodiments may utilize readilyavailable electric power meters, such as a RES+ESS electrical powermeter 32 to measure RES-ESS (e.g., PV+S) facility output, a RESelectrical power meter 19 to measure RES output, and an ESS electricalpower meter 29 to measure ESS output. Signals from the RES electricalpower meter 19 are provided to the RES SCADA controller 12, and signalsfrom the ESS electrical power meter 29 are provided to the ESScontroller 22. The electric power generated by the RES-ESS facility 11may be provided to an electric power system (e.g., an AC electrical grid34) via a generator step-up (GSU) substation 30 that implementsprotection and appropriate voltage conversion. RES transformers 18 andESS transformers 28 may be arranged between the inverters 16, 26,respectively, and the GSU substation 30 to provide voltage conversionutility (e.g., to supply AC power signals to the GSU substation 30 at34.5 kV in certain implementations).

FIG. 1B is a schematic diagram showing certain components of the ACcoupled metering and control system of FIG. 1A, includinginterconnection of control- and sensor-related components. As shown inFIG. 1B, the RES-ESS dispatcher unit 36 is arranged between a utilitycontrol center 38 and a RES-ESS facility 11. Within the RES-ESS facility11, a RES SCADA controller 12 is operatively coupled with RES inverters16A-16N (wherein N represents any suitable number) that are configuredto provide AC conversion of DC power produced by renewable electricalenergy generation units 14A-14N (e.g., arrangeable as parts of arenewable electrical energy generation device 14). Similarly, within theRES-ESS facility 11, an ESS controller 22 is operatively coupled withESS inverters 26A-26N that are configured to provide AC conversion of DCpower supplied by energy storage units 24A-24N (e.g., arrangeable asparts of an energy storage device 24). The RES-ESS facility 11 furtherincludes at least one sensor 40, which may comprise one or more skyimaging sensors useful to determine sky conditions (such as presence ofclouds) proximate to the RES-ESS facility 11, with output signals fromthe at least one sensor 40 being supplied to the RES-ESS dispatcher unit36. The RES-ESS dispatcher unit 36 may also receive: (i) signals fromone or more sensors 42 (e.g., satellite imaging sensors or the like) notnecessarily associated with the RES-ESS facility 11; (ii) meteorologicaldata provided by a meteorological modeling unit 44; (iii) signals from aforecasting unit 46 that may forecast generation by the renewableelectrical energy generation device 14 and/or one or more otherrenewable electrical energy generation devices or units. In certainembodiments, time-dependent forecasting of electrical energy productionmay be performed by the forecasting unit 46 or may be performed by theRES-ESS dispatcher unit 36. In certain embodiments, a time-dependentforecast of electrical energy production may utilize one, two, or allthree of the following: on-site sky imaging provided by the sensor(s)40, satellite imaging provided by the sensor(s) 42, and meteorologicaldata provided by the meteorological modeling unit 44. In certainembodiments, sensors of other types may be used.

FIG. 2 is a block diagram showing for a processor-based energy dispatchcontrol system 50 for dispatching a RES-ESS facility (e.g., includingrenewable electrical energy generation resource and an electrical energystorage device chargeable with electric power produced by the renewableelectrical energy generation resource) according to one embodiment. Thecontrol system 50 includes as functional blocks a utility interface 52,manual inputs 54, a settings combiner 56, and an energy dispatcher 58.The utility interface 52 communicates with an electric power systemutility, and with the energy dispatcher 58 to receive configurationcommands (e.g., CCD mode configuration commands) and send plant statusand state information 62. An example of a CCD mode configuration set bya utility may be a schedule that contains a first SOC target at apre-determined time, and a second SOC target at a second pre-determinedtime. For example, the utility may want the ESS to reach an SOC of 90%by 5:00 PM and an SOC of 10% by 10:00 PM. The utility interface 52receives DNP3 (Distributed Network Protocol) information via a DNP3 link60, and is responsible for converting the published DNP3 configurationpoints to internal data structures. The utility interface 52 is alsoresponsible for communicating any data structure changes back to theutility via the DNP3 link 60. Manual inputs 54 include configurationparameters that are not addressable by MESA-ESS SCADA points. Thesettings combiner 56 validates any configuration inputs and passes themto the energy dispatcher 58 in one implementation. The settings combiner56 receives MESA-ESS schedules/modes/curves provided by a utility orgrid operator, receives schedules produced by an optimizer, and receivesany potential manual inputs 54, and then produces combinedschedules/modes/curves. The energy dispatcher 58 is an engine thatexecutes control modes (including but not limited to coordinatedcharge/discharge or CCD) for the RES-ESS facility (or plant) and decideson the charge or discharge level of the ESS utilizing a renewable energyproduction forecast 64. The energy dispatcher 58 is responsible forcontrolling output of a RES-ESS fin short time scales by observing thecurrent state of the RES-ESS plant, utilizing time-dependent forecastsof electrical energy production by the RES, and utilizing any combinedMESA-ESS schedules/modes/curves produced by the settings combiner 56. Arenewable energy forecast may contain a time series of points for thepower expected to be generated by the renewable energy source (e.g., PVarray, wind turbine, etc.). Such a forecast may have a format of(timestamp, power value) and contain a set of time values of specifiedintervals (e.g., 15 minutes in 1 minute intervals, 36 hours in 1 hourintervals, etc.). These potential formats and timeframes are provided toillustrate the nature of an exemplary forecast, and are not intended tolimit the disclosure. The energy dispatcher 58 is also responsible forpassing alerts and RES-ESS plant state and/or status information back tothe utility interface 52.

In certain embodiments, methods disclosed herein for controlling aRES-ESS plant utilizing a coordinated charge/discharge (CCD) mode maywork simultaneously with other (e.g., PV+S) control algorithms accordingto an amalgamation process. Such an amalgamation processes uses ideal,minimum (lower bound), and maximum (upper bound) values produced by eachcontrol algorithm (wherein each algorithm corresponds to a differentcontrol mode), and based on the configured priority of a controlalgorithm, amalgamation produces a final ESS charge or discharge target.In this regard, in certain embodiments a time-varying charge/dischargecontrol signal is susceptible to being varied by adoption of one or morecontrol modes of multiple control modes, wherein for each control modeof a plurality of control modes, signal candidate values including anupper bound value, a lower bound value, and an ideal value aregenerated. Additionally, an intersection of control signal candidatevalues among multiple control modes is identified, or an ideal value fora control mode of highest priority is selected, to generate thetime-varying charge/discharge control signal. Examples of control modesthat may be utilized in methods disclosed herein include the followingactive power modes specified in the MESA-ESS specification:Charge-Discharge (CD) mode, Coordinated Charge Discharge (CCD) mode,Active Power Limit (APL) mode, Active Power Response (APR) mode, ActivePower Smoothing (APS) mode, Pricing Signal (PS) mode, Volt-Watt (VW)mode, Frequency-Watt Curve (FWC) mode, and Automatic Generation Control(AGC) mode. Such modes will be described hereinafter.

FIGS. 3 and 4 embody logic diagrams for charging and discharging,respectively, of an electrical energy storage device using a system thatincludes a PV array and a battery array chargeable with electric powerproduced by the PV array. Although PV is referenced herein, it is to beappreciated that the disclosed concepts extend to any one or more typesof renewable electrical energy generating units (wind, solar, tidal,etc.) FIGS. 3 and 4 refer to numerous variables. Before describing FIGS.3 and 4 in detail, variables described in such figures are described inthe following Table 1.

TABLE 1 Variable Definition refresh period The time between twoconsecutive executions of the algorithm, wherein BESS_ideal, BESS_minand BESS_max values are held constant during a refresh period (until anext execution of the algorithm) SOC State of charge SOE State of energysoc_to_manage The difference between the target SOC (%) and the currentSOC (%) soe_to_manage soe_to_manage (%) applied to the battery energyrating in Watt-hours pv_production_forecast An array-like objectconsisting of the photovoltaic power production forecast from thecurrent timestep to the SOC target time pv_production_in_periodForecasted PV production during the refresh periodchargeable_pv_forecast Lesser of the current PV production and the BESSnameplate charging capacity chargeable_energy_till_target Sum ofchargeable_pv over the pv production forecast avg_pv_production_forecastArithmetic mean of pv_production_forecast avg_pv_production_in_periodArithmetic mean of pv_production_in_period avg_charge_power Amount ofenergy required to be supplied to a battery to reach a target SOC valuedivided by the number of hours remaining avg_discharge_power Amount ofenergy required to be received from a battery to reach a target SOCvalue divided by the number of hours remaining proportional_charge_powerAverage charge power multiplied by avg_pv_production_in_period and thendivided by the avg_pv_production_forecast proportional_discharge_powerAverage discharge power multiplied by the minimum of (i) avg pvproduction in period divided by the avg_pv_production_forecast and (ii)1 (i.e., the discharge is capped at a multiplier of 1)disch_energy_avail_till_target (ECP interconnection limit (W) × TimeRemaining (H)) - PV energy production in time interval (Wh)

Charging Logic. FIG. 3 is a diagram providing charging logic 100 forcharging an electrical energy storage device to reach a state of charge(SOC) target value using a system that includes a PV array and a batteryarray chargeable with electric power produced by the PV array, accordingto one embodiment. CCD mode runs from a configured start time to aconfigured end time and works to get the ESS to a desired SOC target bya certain time. CCD mode may be executed in a loop inside the energydispatcher and at each refresh period calculates and returns to thecontroller the following three values: BESS_ideal, BESS_max, andBESS_min, as will be described hereinafter, following discussion ofrefresh period.

A refresh period is considered before execution of CCD mode, in order tolimit the ability of RES-ESS facility output to fluctuate except duringspecified time intervals. From a dispatching perspective, limiting theRES-ESS output fluctuations to specified time intervals is attractive topermit an electrical system (e.g., grid) operator to coordinatedifferent generation resources to meet a specified system load, sincevarious generation purchase and supply transactions are commonlyscheduled as firm power outputs for specific (predetermined) blocks oftime. Participation by bidding in energy markets or energy balancemarkets requires firm commitments to supply power for specified periodsof time. To address this issue, a refresh period may be used withsystems and method disclosed herein, with the refresh period beingselected to be a time period convenient for a system operator (e.g., 15minutes, 30 minutes, or another selectable time interval). A refreshperiod corresponds to a time between two consecutive executions of aRES-ESS control algorithm (e.g., for establishment of new basepointvalues). BESS_min, BESS_ideal, and BESS_max values are recalculated onceupon the expiration of a refresh period, but after such values arerecalculated, they remain constant until expiration of the next refreshperiod. This is shown in FIG. 3 . Decision block 102 considers whetherthe current time matches the refresh frequency. If the query in decisionblock 102 is false (i.e., the current refresh period has not yet ended),then values for each of BESS_min, BESS_ideal, and BESS-max remainunchanged (i.e., BESS_min remains the previously computed Min set-pointat block 102, BESS_ideal remains the previously computed Ideal set-pointat block 104, and BESS_max remains the previously computed Max set-pointat block 106). If the query in decision block 102 is true (i.e., thecurrent refresh period has ended), then values for each of BESS_min,BESS_ideal, and BESS_max may be recalculated, starting at decision block110.

Bess_Ideal Calculation. Decision block 110 considers whether a forecastis available. If a forecast is available (i.e., the inquiry at decisionblock 110 is true), then the BESS prioritizes charging at times when thePV generation is higher, and BESS_min, BESS_ideal, and BESS_max arecomputed at blocks 112, 114, and 116, respectively. At block 114,BESS_ideal is set to the minimum of proportional_charge_power and BESSnameplate discharge power capacity. In implementations wherein gridcharging is not permitted, the highest charging level that can beobtained is equal to the power generated from PV. If a forecast is notavailable (i.e., the inquiry at decision block 110 is false), then incertain embodiments the BESS performs “greedy charging” by charging theentire chargeable_pv at every timestep. In certain embodiments, if aforecast is not available, the BESS_ideal set-point is the minimum ofSOE to manage in Wh or BESS nameplate discharge power capacity, asindicated at block 122.

BESS_max Calculation. In certain embodiments, the BESS_max powerset-point for CCD is the same as the BESS_ideal power set-point if theamount of energy available is less than the amount of energy required toreach the SOC target. In certain embodiments, the BESS_max powerset-point is the nameplate discharge power capacity of the BESS, asindicated at block 116. If a forecast is not available (i.e., theinquiry at decision block 110 is false), then the BESS_max powerset-point is the BESS nameplate discharge power capacity, as indicatedat block 124.

BESS_min Calculation. If a forecast is available (i.e., the inquiry atdecision block 110 is true), then the BESS_min power set-point forcharging (most negative power set-point) is the minimum of (i) (ECPinterconnection limit (in Watts) times Time Remaining (in Hours)) minusPV energy production in time interval (in Watt hours) plus SOE to manage(in Watt hours), (ii) Bess nameplate discharge power, or (iii)Bess_ideal setpoint of this mode, as indicated at block 112. If aforecast is not available (i.e., the inquiry at decision block 110 isfalse), then the BESS_min power set-point is the minimum of SOE tomanage in Wh or BESS nameplate discharge power capacity, as indicated atblock 120.

Discharging Logic. FIG. 4 is a diagram providing discharging logic 130for discharging an electrical energy storage device using a system thatincludes a PV array and a battery array chargeable with electric powerproduced by the PV array according to one embodiment. As before, arefresh period is considered before execution of CCD mode, in order tolimit the ability of RES-ESS facility output to fluctuate except duringspecified time intervals. As shown in FIG. 4 , decision block 132considers whether the current time matches the refresh frequency. If thequery in decision block 132 is false (i.e., the current refresh periodhas not yet ended), then values for each of BESS_min, BESS_ideal, andBESS_max remain unchanged (i.e., BESS_min remains the previouslycomputed Min set-point at block 134, BESS_ideal remains the previouslycomputed Ideal set-point at block 136, and BESS_max remains thepreviously computed Max set-point at block 138). If the query indecision block 132 is true (i.e., the current refresh period has ended),then values for each of BESS_min, BESS_ideal, and BESS_max may berecalculated, starting at decision block 140.

With continued reference to FIG. 4 , CCD mode runs from a configuredstart time to a configured end time and works to get the ESS to adesired SOC target by a certain time. CCD mode may be executed in a loopinside the energy dispatcher and at each refresh period calculates andreturns to the controller the following three values: Bess_Ideal,Bess_Max, and Bess_Min, as will be described below.

BESS_ideal Calculation. Decision block 140 considers whether a forecastis available. If a forecast is available (i.e., the inquiry at decisionblock 140 is true), then the BESS prioritizes discharging at times whenthe PV generation is lower, and BESS_min, BESS_ideal, and BESS_max arecomputed at blocks 142, 144, and 146, respectively. At block 144,Bess_ideal is set to the minimum of chargeable PV andproportional_charge_power. If the discharging period is not during theday, then the BESS_ideal power setpoint would be the avgdischarge_power. If a forecast is not available (i.e., the inquiry atdecision block 140 is false), the Ideal BESS discharge power setpointwould be chargeable_pv, as indicated at block 154.

BESS_min Calculation. Regardless of whether a forecast is available(i.e., if the inquiry at decision block 140 is true or false), theBESS_min power setpoint would be the minimum of (i) SOE_to_Manage (inWatt-hours) or chargeable_PV, as indicated at blocks 142 and 152.

BESS_max Calculation. If a forecast is available (i.e., the inquiry atdecision block 140 is true), then logic proceeds to decision block 146,which presents an inquiry whether available_energy is less than or equalto SOE_to_manage. If the inquiry at decision block 146 is true, then theBESS_max power setpoint would be the minimum of chargeable PV andproportional_charge_power, as indicated at block 148. If the inquiry atdecision block 146 is false, then the BESS_max power setpoint would bethe BESS discharging power nameplate capacity, as indicated at block150. Turning back to decision block 140, if the inquiry at decisionblock 140 is false, then the BESS_max power setpoint would bechargeable_pv, as indicated at block 156.

FIG. 5 is an exemplary output plot for system including a renewableelectrical energy generation resource (RES) and an electrical energystorage device (e.g., a battery energy storage system or BESS)chargeable with electric power produced by the renewable electricalenergy generation resource, when controlled by a method as disclosedherein, for a period between 06:00 and 21:00 of a single day. The outputplot includes PV generation in megawatts (PV MW), state of charge of thebattery energy storage system (BESS SOC), and aggregated photovoltaicplus storage energy supplied to an electric grid (PV+S Output). A SOCschedule requires attainment of 80% SOC for the BESS by 12:00, and 0%SOC by 20:00 (8:00 PM). A charging algorithm is employed from about07:00 to 12:00, and a discharging algorithm is employed from 12:00 to20:00. While the charging algorithm is employed, PV MW is notnecessarily the PV+S Output, since a portion of the PV generation isallocated to charge the BESS. The SOC of the BESS rises from 07:00 to12:00, but not at a linear rate. As shown by the dashed vertical lineswith arrow ends, while the charging algorithm is in use, a greateramount of BESS charging results when more PV generation is available,and a lesser amount of BESS charging results when less PV generation isavailable. Conversely, while the discharging algorithm is in use, alesser amount of energy is discharged from the BESS when more PVgeneration is available, and a greater amount of energy is dischargedfrom the BESS when less PV generation is available.

As noted previously herein, the MESA-ESS specification describes thefollowing active power modes: [1] Charge-Discharge (CD) mode, [2]Coordinated Charge-Discharge (CCD) mode, [3] Active Power Limit (APL)mode, [4] Active Power Response (APR) mode, [5] Active Power Smoothing(APS) mode, [6] Pricing Signal (PS) mode, [7] Volt-Watt (VW) mode, [8]Frequency-Watt Curve (FWC) mode, and [9] Automatic Generation Control(AGC) mode. Modes [1] to [6] result in a battery active power outputthat may be called a “basepoint,” such that modes [1] to [6] may betermed basepoint modes. Modes [7] to [9] are “additive” modes that addpositive or negative power to the basepoint, and may be termednon-basepoint modes. A unique characteristic of the non-basepoint modesis that APS mode will not consider the resultant added power from themwhen calculating the next basepoint.

The MESA-ESS specification delineates how different active power controlmodes should function and identifies the possibility of combining them,but such document does not attempt to define how the functionality ofdifferent control modes can be combined or stacked. Each active mode canusually be satisfied with a range of power responses at any given time.For example, if a 4 hour battery (e.g., that is chargeable from 0% to100% in 4 hours) has an 8 hour window in which the battery is to becharged, the battery could charge all in the beginning, all at the end,or evenly throughout the 8 hour window. This flexibility can beleveraged to implement multiple modes at the same time, such as a chargewindow and smoothing solar power generation. Amalgamation processesdescribed herein enable different MESA-ESS active power control modes tobe combined to produce an output that accommodates the respectivecontrol modes if they are compatible, while also allowing each controlmode to be prioritized relative to the other control mode.

As introduced previously herein, an algorithm dedicated to each activepower control mode may output an ideal value, a minimum (lowerbound—corresponding to the most negative or least positive) value, and amaximum (upper bound—corresponding to the most positive or leastnegative) value that can be accommodated by a BESS while the still beingable to satisfy defined requirements (e.g., according to a SOCschedule). In certain embodiments, such values embody power setpointsthat may be defined with respect to a BESS meter, whereby a negativevalue represents charging and a positive value represents discharging.The ideal BESS power setpoint for each mode represents the preferredactive power requirement for it to operate most efficiently in order toperform its function. The three setpoints (ideal, minimum, and maximum)could mean different things for different active power control modes.For example, for Coordinated Charge Discharge Management (CCD) mode, theMin and Max BESS power setpoints would represent the minimum and maximumBESS power, respectively, that the mode can accommodate at that instantwhile satisfaction of a SOC target is still attained. The ideal powersetpoint could be defined as the required BESS active power to reach theSOC target in an optimal fashion.

For Active Power Limiting control mode that limits the power below acertain active power limit, the BESS_max power setpoint would be themaximum power the control mode can accommodate (i.e., a powerthreshold), while the minimum BESS power setpoint for this case could bethe minimum operating limit of the RES-ESS plant since the control modedoes not have a set lower limit threshold.

Mode-stacking may be performed by connecting different control modes inseries. This may be implemented by passing the Min, Max, and Idealsetpoints of one control mode to the next control mode in order ofpriority of the respective control mode. The control mode next in seriesmay use the setpoint values of the previous control mode in itscomputation, and then output its own setpoint values.

FIG. 6 is a first diagram illustrating a serial (or stacking)arrangement of different control modes 162, 164, 166 usable by a controlsystem 160, with each control mode including multiple control signalcandidate values, and with the serially connected control modesproducing a single active power command. The highest priority, stagingmode 162 consists of the operating limits of the BESS and is always thehighest priority (e.g., Priority 0). All control modes should operatewithin the limit (Min and Max) defined by the staging mode 162. Stackingcontrol modes sequentially tests whether a lower priority mode'srequirement is within the limits of a higher priority mode. If the lowerpriority mode is out of bounds, then the setpoints of the higherpriority mode get preference by overriding setpoints of the lowerpriority mode. As shown, the next highest priority modes are CCD mode164 and APS mode 166, respectively. A basepoint signal 168 is generatedby identifying an intersection of control signal candidate values amongthe multiple control modes 162, 164, 166, or selecting an ideal valuefor a control mode 162, 164, 166 of highest priority, and in the presentembodiment the basepoint signal 168 serves as a time-varyingcharge/discharge control signal (e.g., an active power command signal)169 usable for controlling one or more components of a RES-ESS facility.

As noted previously, the staging mode is by default the highest prioritymode and contains the present operating limits of the ESS (e.g., BESS).The Min and Max of this mode are calculated using the currentoperational state and conditions of the ESS. Examples of limitsaddressed by staging mode include fundamental system limits (e.g.,energy source or self-imposed limits), nameplate and device limits(e.g., nameplate maximum voltage rating and nameplate active generationpower rating at unity power factor)), and present operating limits(e.g., maximum voltage and maximum active generation power). As anexample of energy source of self-imposed limits, consider that a systemcannot produce power that it does not have available, and that limits onwattage may result from availability on solar resources and/or limits aninverter imposes on itself due to factors such as thermal conditions,errors, failures, etc.

FIGS. 7A-7E embody tables identifying control signal candidate valuesfor multiple serially connected control modes and a net output valueaccording to five different examples. In FIG. 7A, all control modes arewithin the bounds set by the higher priority mode, and a value of −20 MWis selected as the basepoint net output. In FIG. 7B, all control modesare outside the bounds set by the higher priority mode, and a value of 0MW is selected as the basepoint net output. In FIG. 7C, all controlmodes partially overlap, and a value of 10 MW is selected as thebasepoint net output. In FIG. 7D, the higher priority CCD mode canpartially accommodate the lower priority APS mode, and a value of 10 MWis selected as the basepoint net output. In FIG. 7E, the higher priorityCCD mode and lower priority APS mode setpoints conflict with oneanother, such that the value within CCD mode range and closest to theAPS mode range (namely, 0 MW) is selected as the basepoint net output.

In certain embodiments, different control modes (or combinations ofcontrol modes) may be operated at different times.

FIG. 8 is an exemplary output plot for system including a renewableelectrical energy generation resource (e.g., a PV source) and anelectrical energy storage device (e.g., a BESS) chargeable with electricpower produced by the renewable electrical energy generation resource,when controlled by a method utilizing different combinations ofconnected control modes at different times according to one embodiment.The output plot includes PV generation in megawatts (PV MW)), state ofcharge of the battery energy storage system (BESS SOC), and aggregatedphotovoltaic plus storage energy supplied to an electric grid (PV+SOutput). Active Power Smoothing (APS) mode plus CoordinatedCharge-Discharge (CCD) mode are enabled at sunrise (about 07:00) toreach 50% SOC by 12:00. Only APS mode is enabled from 12:00 until 14:30.Only CCD mode is enabled at sunset (about 17:00) to reach 0% SOC by21:00. As shown in FIG. 8 , combined PV+S output exhibits lesspeak-to-trough variation than PV MW during periods of significant PV MWfluctuation (e.g., from 08:00 through 14:00).

APS is a basepoint control mode that smooths PV+S plant output based ona specified Electrical Connection Point (ECP) reference meter signal. Incertain embodiments, APS may involve measuring current PV+S output atthe point of interconnect with a grid, calculating a moving average ofthe ECP reference meter based on an APS filter time, calculatingadditional watts required based on (i) a deadband (extending ahead andbehind of the moving average of reference power), (ii) a smoothinggradient, and (iii) the moving average of the ECP reference meter.

FIG. 9 is a second diagram illustrating a serial (or stacking)arrangement of different control modes 172, 174, 176, 180, 182 usable bya control system 170. The control system 170 utilizes serially connectedbasepoint control modes 172, 174, 176 and non-basepoint control modes180, 182 that produce a single active power command. Each control mode172, 174, 176, 180, 182 includes multiple control signal candidatevalues. The highest priority, staging mode 172 consists of the operatinglimits of the BESS, and is followed (in decreasing priority) by CCD mode172 and APS mode 174, respectively, to yield a basepoint value 178. Thebasepoint value 178 is generated by identifying an intersection ofcontrol signal candidate values among the preceding control modes 172,174, 176, or selecting an ideal value for the preceding control mode ofhighest priority. This basepoint value 178 is modified (e.g., increasedor decreased) by serial application of the Automatic Generation Control(AGC) mode 180 and Frequency-Watt Curve (FWC) mode 182, respectively. Atime-varying charge/discharge control signal (e.g., an active powercommand signal) 183 results from modification of the basepoint value 178with non-basepoint values generated by the AGC and FWC modes 180, 182.FIG. 9 therefore illustrates how AGC and FWC modes 180, 182 may addpower to the basepoint. A typical implementation of additive modes mayassume that some power from the BESS is reserved from the calculation ofthe basepoint value 178. For example, a 20 MW BESS may have 2 MWreserved for AGC and FWC modes. Therefore the staging mode (priority 0)would only see −18 to 18 MW available. In one implementation, abasepoint value of −18 MW may be calculated, AGC mode may yield 2 MW,and FWC mode may yield −1 MW. An active power command of −17 MW mayresult (calculated as (−18)+(2)+(−1)). AGC mode is an additive powercontrol mode that outputs a single PV+S power setpoint based on anactive power target set by the master, wherein the AGC output is addedon top of the basepoint value, subject to operating limit constraints ofa RES-ESS (e.g., PV+S) facility.

FWC mode is an additive power control mode used to alter a system'spower output in response to measured deviation from a specified nominalfrequency. In certain embodiments, FWC may involve measuring gridfrequency using the reference EPC meter. If the grid frequency is withina specified deadband or if the current BESS SOC is outside allowedusable SOC limits, then no action is performed. However, if the gridfrequency is outside a specified deadband, then additional power to beprovided is calculated using a measured droop.

In certain embodiments, ramp rate constraints may be applied to acontrol signal for a RES-ESS facility, wherein forecasted RES producedmay be examined at every timestep, and power may be curtailedpreemptively in order to mitigate RES production ramp down events (e.g.,sudden dips in PV production). Ramp rate in this context may be definedas the change in power output of a RES facility or RES-ESS facility(e.g., PV+S facility) in a given time interval (e.g., change per minuteor change per hour). Leveraging of short-term RES production forecastsmay be used. The two main ramping events subject to control are (1) rampdown events, and (2) ramp up events. Ramp-down events in the context ofa facility including PV production may be mitigated by obtaining aforecast for future PV from the current time to ‘f’ minutes in thefuture, wherein ‘f’ is a function of a ramp rate down limit. A gradientor slope between the current plant production and the forecasted PVpower values may be calculated and compared with a defined ramp ratedown limit. If the gradients of future power values are not within theramp rate down limit, then PV power may be curtailed by an amount equalto the minimum gradient in the current forecast time series. If thegradients of future power values are within the ramp rate down limit,then no corrective action is necessary.

Controlling ramp rate up events is simpler. At every timestep, currentRES (e.g., PV) production is compared with the plant production in theprevious timestep. If the plant production is less than the current RESproduction, then curtailment is applied to make sure that the RES plantoutput does not violate the ramp limit. This function may be performedby inverters at the RES-ESS plant. This may be applied in two instances.Firstly, if there is a sudden increase in RES production, this logicwill control plant production so that total output increases in steps ofpower that are less than equal to the ramp rate up limit. Secondly, ifenergy had been curtailed in the previous timestep to sustain a ramprate down event, the RES-ESS plant output is increased by no greaterthan the ramp rate up limit in order to bring the curtailment back tozero. After ramp rate up curtailment power has been calculated,gradients to forecasted RES production values are recalculated for theramp-up curtailment. If the result of the current ramp rate up eventcauses uncontrollable violations in the future, then an optimalcurtailment solution is obtained so that all future violations arecontrolled.

FIG. 10 is schematic diagram of a generalized representation of acomputer system 200 that can be included as one or more components of asystem for controlling a renewable electrical energy generation resourceand an electrical energy storage device chargeable with electric powerproduced by the renewable electrical energy generation resource,according to one embodiment. The computer system 200 may be adapted toexecute instructions from a computer-readable medium to perform theseand/or any of the functions or processing described herein.

The computer system 200 may include a set of instructions that may beexecuted to program and configure programmable digital signal processingcircuits for supporting scaling of supported communications services.The computer system 200 may be connected (e.g., networked) to othermachines in a local area network (LAN), an intranet, an extranet, or theInternet. While only a single device is illustrated, the term “device”shall also be taken to include any collection of devices thatindividually or jointly execute a set (or multiple sets) of instructionsto perform any one or more of the methodologies discussed herein. Thecomputer system 200 may be a circuit or circuits included in anelectronic board or card, such as a printed circuit board (PCB), aserver, a personal computer, a desktop computer, a laptop computer, apersonal digital assistant (PDA), a computing pad, a mobile device, orany other device, and may represent, for example, a server or a user'scomputer.

The computer system 200 in this embodiment includes a processing deviceor processor 202, a main memory 204 (e.g., read-only memory (ROM), flashmemory, dynamic random access memory (DRAM), such as synchronous DRAM(SDRAM), etc.), and a static memory 206 (e.g., flash memory, staticrandom access memory (SRAM), etc.), which may communicate with eachother via a data bus 208. Alternatively, the processing device 202 maybe connected to the main memory 204 and/or static memory 206 directly orvia some other connectivity means. The processing device 202 may be acontroller, and the main memory 204 or static memory 206 may be any typeof memory.

The processing device 202 represents one or more general-purposeprocessing devices, such as a microprocessor, central processing unit(CPU), or the like. In certain embodiments, the processing device 202may be a complex instruction set computing (CISC) microprocessor, areduced instruction set computing (RISC) microprocessor, a very longinstruction word (VLIW) microprocessor, a processor implementing otherinstruction sets, or other processors implementing a combination ofinstruction sets. The processing device 202 is configured to executeprocessing logic in instructions for performing the operations and stepsdiscussed herein.

The computer system 200 may further include a network interface device210. The computer system 200 may additionally include at least one input212, configured to receive input and selections to be communicated tothe computer system 200 when executing instructions. The computer system200 also may include an output 214, including but not limited to adisplay, a video display unit (e.g., a liquid crystal display (LCD) or acathode ray tube (CRT)), an alphanumeric input device (e.g., akeyboard), and/or a cursor control device (e.g., a mouse).

The computer system 200 may or may not include a data storage devicethat includes instructions 216 stored in a computer readable medium 218.The instructions 216 may also reside, completely or at least partially,within the main memory 204 and/or within the processing device 202during execution thereof by the computer system 200, the main memory 204and the processing device 202 also constituting computer readablemedium. The instructions 216 may further be transmitted or received overa network 220 via the network interface device 210.

While the computer readable medium 218 is shown in an embodiment to be asingle medium, the term “computer-readable medium” should be taken toinclude a single medium or multiple media (e.g., a centralized ordistributed database, and/or associated caches and servers) that storethe one or more sets of instructions. The term “computer readablemedium” shall also be taken to include any medium that is capable ofstoring, encoding, or carrying a set of instructions for execution bythe processing device and that cause the processing device to performany one or more of the methodologies of the embodiments disclosedherein. The term “computer readable medium” shall accordingly be takento include, but not be limited to, solid-state memories, an opticalmedium, and/or a magnetic medium.

In certain embodiments, systems and apparatuses disclosed herein mayutilize a non-transitory computer readable medium containing programinstructions for controlling, by at least one processor, (i) a renewableelectrical energy generation resource and (ii) an electrical energystorage device chargeable with electric power produced by the renewableelectrical energy generation resource, the method comprising utilizing,by the at least one processor, (A) a time-dependent forecast ofelectrical energy production by the renewable electrical energygeneration resource and (B) a state of charge (SOC) schedule for theelectrical energy storage device including at least one SOC targetvalue, to generate a time-varying charge/discharge control signal forthe electrical energy storage device, wherein the time-varyingcharge/discharge control signal is configured to ensure that the SOCschedule is satisfied by charging at the average rate necessary to meetthe SOC target schedule, while periodically updating the generation ofthe time-varying charge/discharge control signal based upon at least oneof an updated time-dependent forecast of electrical energy production oran updated SOC schedule. In certain embodiments, the programinstructions contained in the computer readable medium may be configuredto perform additional method steps as disclosed herein.

FIGS. 11A and 11B are provided to permit visual comparison of theeffects of not utilizing versus utilizing a refresh period to limitrecalculation of basepoint values for controlling aggregate output of aRES-ESS facility. FIG. 11A is a modeled output plot for a systemincluding a renewable electrical energy generation resource (RES) in theform of PV and an electrical energy storage device (ESS) chargeable withelectric power produced by the renewable electrical energy generationresource, when controlled by a method as disclosed herein but without aconfigurable refresh period, for a period including 06:00 to 21:00 of asingle day. Significant temporal fluctuation in aggregated photovoltaicplus storage (PV+S) output is shown between 09:00 and 18:00, with veryfew time periods having a non zero slope that would correspond toconstant power output. These fluctuations in plant output would inhibitthe ability of a plant operator to participate by bidding to supplyfixed blocks of power for specified periods of time in energy marketsand/or energy balance markets.

FIG. 11B is a modeled output plot for the same RES-ESS system and perioddepicted in FIG. 11A, when controlled by a method disclosed herein withutilization of a 30 minute refresh period, in which basepoint value isrecalculated once every 30 minutes. As shown, the aggregated PV+S outputremains substantially constant for each 30 minute time period, since thebasepoint control value remains constant during each 30 minute refreshperiod. The application of a refresh period for coordinate control of aRES-ESS facility enables the plant to supply fixed blocks of power forspecified time periods, thereby permitting the plant operator toparticipate by bidding to supply fixed blocks of power for specifiedperiods of time in energy markets and/or energy balance markets.

FIGS. 12A and 12B provided modeled output plots for a system including arenewable electrical energy generation resource (RES) (e.g., PV) and anelectrical energy storage device (ESS) chargeable with electric powerproduced by the RES. The output plots of FIGS. 12A and 12B exhibitutilization of a refresh period, but only the output plot of FIG. 12Bavoids an undesirable valley in aggregated plant (PV+S) output afterdaily PV production has ended, followed by an increase in PV+S outputduring discharge of the ESS. The output plot of FIG. 12A corresponds toa control scheme that utilizes a SOC compliance evaluation period thatconsiders only hours remaining the day for each time period—namely, fromthe current time to an end of day SOC target (e.g., 22:00 hours in eachfigure). The limitation of this approach is that it may not discharge anESS rapidly enough when RES (e.g., PV) production drops and stays lowthrough the end of a day. Additionally, the approach in FIG. 12A leadsto a diminishing average power problem. When the window is updated to besmaller and smaller as the current time increments and the end of thewindow remains constant, during a natural ramp down the average tends toalways be lower than the current power. This results in the algorithmestimating a lower basepoint and causes the valley 252 that is apparentin FIG. 12A. Although a zero SOC target is attained at 22:00 in each ofFIGS. 12A and 12B, and each figure is substantially identical from thestart of day until about 17:00, the output plots of FIGS. 12A and 12Bdiffer significantly between 17:00 and 22:00. FIG. 12A provides a PV+Sprofile 250 between 17:00 and 22:00 that includes a valley region 251 inwhich PV+S output declines to a minimum of about 22 MW followed by aPV+S increase region 254 in which PV+S output is increased to a value ofnearly 50 MW before declining rapidly to zero at 22:00. In contrast,FIG. 12B provides a different PV+S profile 255 that is devoid of anyvalleys followed by positive slope regions that would correspond toincreases in PV+S output. In particular, the PV+S profile 255 shown inFIG. 12B decreases in a substantially stepwise manner between 17:00 and22:00, with a final drop from about 30 MW to zero at 22:00. Thisimproved PV+S profile 255 shown in FIG. 12B may be attained byutilization of a static window instead of a dynamic window for meetingan end of day SOC target. Furthermore, while the window length isstatic, the forecasted power values in the window are updated as thefacility receives updated forecasts. While specific aspects, featuresand illustrative embodiments have been disclosed herein, it will beappreciated that the disclosure extends to and encompasses numerousother variations, modifications, and alternative embodiments, as willsuggest themselves to those of ordinary skill in the pertinent art,based on the disclosure herein. Various combinations andsub-combinations of the structures described herein are contemplated andwill be apparent to a skilled person having knowledge of thisdisclosure. Any of the various features and elements as disclosed hereinmay be combined with one or more other disclosed features and elementsunless indicated to the contrary herein. Correspondingly, the inventionas hereinafter claimed is intended to be broadly construed andinterpreted, as including all such variations, modifications andalternative embodiments, within its scope and including equivalents ofthe claims.

What is claimed is:
 1. A method comprising: obtaining a state of charge(SOC) schedule for an energy storage device and a time-dependentforecast of electrical energy production by a renewable electricalenergy generation resource, wherein the SOC schedule defines an SOCtarget for each of a plurality of time periods; generating atime-varying charge/discharge control signal for the electrical energystorage device based on the time-dependent forecast of electrical energyproduction, wherein the time-varying charge/discharge control signal isconfigured to maintain an average SOC of the energy storage device aslow as possible while satisfying the SOC target for each of theplurality of time periods of the SOC schedule; and controlling chargingand discharging of the energy storage device with the time-varyingcharge/discharge control signal.
 2. The method of claim 1, wherein thetime varying charge/discharge control signal is configured to maintainthe average SOC of the energy storage device while charging only fromthe renewable electrical energy generation resource.
 3. The method ofclaim 1, further comprising periodically updating the generation of thetime-varying control signal upon expiration of a refresh period, whereinthe periodic updating comprises computing and using a new basepointvalue for aggregated energy supplied from the renewable electricalenergy generation resource and the electrical energy storage device toan electrical grid upon expiration of the refresh period.
 4. The methodof claim 1, further comprising altering the time-varyingcharge/discharge control signal responsive to a difference betweenforecasted production and actual production of at least one electricgeneration facility to ensure that the SOC schedule is satisfied.
 5. Themethod of claim 1, wherein the time-varying charge/discharge controlsignal is further configured to increase a value of the time-varyingcharge/discharge control signal during periods of increased relativeproduction of the renewable electrical energy generation resource tosmooth an aggregated power output supplied to an electrical grid by therenewable electrical energy generation resource and the electricalenergy storage device, while ensuring that the SOC schedule issatisfied.
 6. The method of claim 1, wherein the time-varyingcharge/discharge control signal is susceptible to being varied byadoption of one or more control modes of a plurality of control modes,and wherein the method further comprises: for each control mode of theplurality of control modes, generating a plurality of control signalcandidate values including an upper bound value, a lower bound value,and an ideal value; and identifying an intersection of control signalcandidate values among multiple control modes, or selecting an idealvalue for a control mode of highest priority, to generate thetime-varying charge/discharge control signal.
 7. The method of claim 6,wherein the plurality of control modes comprises two or more of thefollowing modes: Charge-Discharge mode, Coordinate Charge Dischargemode, Active Power Limit mode, Active Power Response mode, Active PowerSmoothing mode, and Pricing Signal mode.
 8. The method of claim 7,wherein the plurality of control modes further comprises at least one ofthe following modes: Volt-Watt mode, Frequency-Watt Curve mode, andAutomatic Generation Control mode.
 9. The method of claim 1, wherein therenewable electrical energy generation resource comprises a photovoltaicarray, the electrical energy storage device comprises a battery array,and the time-dependent forecast of electrical energy productioncomprises a solar production forecast.
 10. The method of claim 1,wherein the renewable electrical energy generation resource comprises atleast one wind turbine, the electrical energy storage device comprises abattery array, and the time-dependent forecast of electrical energyproduction comprises a wind production forecast.
 11. The method of claim1, wherein the time-dependent forecast of electrical energy productioncomprises an ensemble based on of two or more of the following: on-sitesky imaging, satellite imaging, and meteorological modeling.
 12. Anon-transitory computer readable medium comprising instructions storedthereon that, when executed by a processor, cause the processor toperform operations comprising: obtaining a state of charge (SOC)schedule for an energy storage device and a time-dependent forecast ofelectrical energy production by a renewable electrical energy generationresource, wherein the SOC schedule defines an SOC target for each of aplurality of time periods; generating a time-varying charge/dischargecontrol signal for the electrical energy storage device based on thetime-dependent forecast of electrical energy production, wherein thetime-varying charge/discharge control signal is configured to maintainan average SOC of the energy storage device as low as possible whilesatisfying the SOC target for each of the plurality of time periods ofthe SOC schedule; and controlling charging and discharging of the energystorage device with the time-varying charge/discharge control signal.13. The method of claim 12, wherein the time varying charge/dischargecontrol signal is configured to maintain the average SOC of the energystorage device while charging only from the renewable electrical energygeneration resource.
 14. The non-transitory computer readable medium ofclaim 12, wherein the time-varying charge/discharge control signal isfurther configured to increase a value of the time-varyingcharge/discharge control signal during periods of increased relativeproduction of the renewable electrical energy generation resource tosmooth an aggregated power output supplied to an electrical grid by therenewable electrical energy generation resource and the electricalenergy storage device, while ensuring that the SOC schedule issatisfied.
 15. The non-transitory computer readable medium of claim 12,wherein the time-varying charge/discharge control signal is susceptibleto being varied by adoption of one or more control modes of a pluralityof control modes, and wherein the operations further comprise: for eachcontrol mode of the plurality of control modes, generating a pluralityof control signal candidate values including an upper bound value, alower bound value, and an ideal value; and identifying an intersectionof control signal candidate values among multiple control modes, orselecting an ideal value for a control mode of highest priority, togenerate the time-varying charge/discharge control signal.
 16. Thenon-transitory computer readable medium of claim 15, wherein theplurality of control modes comprises two or more of the following modes:Charge-Discharge mode, Coordinate Charge Discharge mode, Active PowerLimit mode, Active Power Response mode, Active Power Smoothing mode, andPricing Signal mode.
 17. The non-transitory computer readable medium ofclaim 15, wherein the plurality of control modes further comprises atleast one of the following modes: Volt-Watt mode, Frequency-Watt Curvemode, and Automatic Generation Control mode.
 18. The non-transitorycomputer readable medium of claim 12, wherein the renewable electricalenergy generation resource comprises a photovoltaic array, theelectrical energy storage device comprises a battery array, and thetime-dependent forecast of electrical energy production comprises asolar production forecast.
 19. A system comprising: a processor coupledwith memory, the processor configured to: obtain a state of charge (SOC)schedule for an energy storage device and a time-dependent forecast ofelectrical energy production by a renewable electrical energy generationresource, wherein the SOC schedule defines an SOC target for each of aplurality of time periods; generate a time-varying charge/dischargecontrol signal for the electrical energy storage device based on thetime-dependent forecast of electrical energy production, wherein thetime-varying charge/discharge control signal is configured to maintainan average SOC of the energy storage device as low as possible whilesatisfying the SOC target for each of the plurality of time periods ofthe SOC schedule; and control charging and discharging of the energystorage device with the time-varying charge/discharge control signal.20. The system of claim 19, wherein the time varying charge/dischargecontrol signal is configured to maintain the average SOC of the energystorage device while charging only from the renewable electrical energygeneration resource energy source.